1. Field of the Invention
This invention relates to a high pressure fuel injection tubing material to be used generally for fuel feeding lines of diesel engines and to a method of manufacturing the same.
2. Description of the Prior Art
In the high pressure fuel injection tubing material in the prior art shown, for example, in "Fuel Injection Tubing"--SAE on pages 21.123 to 21.124 of the SAE Standards and "Testing Technique for Diesel Fuel Injection Systems"--SAE Recommended Practice on pages 24.91 to 24.96 of SAE Journal 969a, the hardened grain structure produced over the entire tube wall by cold drawing by repeatedly using dies and plugs is uniformly removed by tempering so that the carbon content and hardness distribution (of Hv=about 110 to 120) may be substantially uniform over the entire tube wall and no residual compression stress may be seen in the finally finished tube diameter to be used.
Therefore, due the actual state of the generation of numerous hair cracks on the inside surface with such repeated cold drawing works, the uniform structure by tempering the entire tubing material under the state of the final uniform carbon content distribution and the section structure in which no residual compression stress is present and, on the other hand, as a multiplied effect of the very high internal flow pressure in the recent tendency and the flow pressure variation and vibration variation repeated constantly by the operating state of the engine, the inside surface will be eroded by a cavitation, will be reduced in the smoothness and true circularity and will be locally cracked or broken by such erosion at last. At the same time, in order to prevent them and to secure safety, a large diameter tubing material with the increase of the wall thickness is inevitably forced to be used but the effect can not be well expected. Generally no sufficient mechanical property as of an injection tubing material can be secured and therefore the improvement has been constantly hoped for.